During the World War II years, he served in the United States Army.
One year prior to his death, he published his first and only novel, a work titled Stewart Lane.
Born Francesco Stallone in southern Italy, he relocated to the United States with his family when he was thirteen years old. He and his three siblings were the children of Silvestro Stallone.
Sylvester and Frank Stallone, Jr. are Frank Stallone, Sr.'s sons through his marriage to dancer and astrologer Jackie Stallone. He was married three more times (to Rose Marie Stallone, Sandra Stallone, and Kathleen Rhodes), and he fathered three additional children (Bryan, Carla, and Dante).